Academic literature on the topic 'Soil δ¹⁵N'

Petroleum contamination in terrestrial environments caused by industrial activities is a significant problem that has received considerable attention. Carbon and nitrogen isotopic compositions (δ¹³C and δ¹⁵N) effectively describe the behavior of plants and soils under petroleum contamination stress. To better understand plant and soil responses to petroleum-contaminated soil, δ¹³C and δ¹⁵N values of the plants (<i>Agropyron cristatum</i>, Leguminosae with C₄ photosynthesis pathway, and <i>Trifolium repens</i> with C₃ photosynthesis pathway) and the soil samples under 1-month exposure to different extents of petroleum contamination were measured. The results showed that petroleum contamination in the soil induced the soil δ¹⁵N values to increase and δ¹³C values to decrease; from 1.9 to 3.2 ‰ and from −23.6 to −26.8 ‰, respectively. However, the δ¹³C values of <i>Agropyron cristatum</i> decreased from −29.8 ‰ to −31.6 %, and the δ¹³C values of<i> Trifolium repens</i> remained relatively stable from −12.6 ‰ to −13.1 ‰, indicating that they have different coping strategies under petroleum-contaminated soil conditions. Moreover, the δ¹⁵N values of <i>Trifolium repens</i> decreased from 5.6 ‰ to 0.8 ‰ near the air δ¹⁵N values under petroleum-contaminated soil, which implies that their nitrogen fixation system works to reduce soil petroleum stress. The δ¹³C and δ¹⁵N values of <i>Agropyron cristatum</i> and <i>Trifolium repens</i> reflect changes in the metabolic system when they confront stressful environments. Therefore, stable isotopic compositions are useful proxies for monitoring petroleum-contaminated soil and evaluating the response of plants to petroleum contamination stress.

Terrestrial carbon cycling is largely mediated by soil food webs. Identifying the carbon source for soil animals has been desired to distinguish their roles in carbon cycling, but it is challenging for small invertebrates at low trophic levels because of methodological limitations. Here, we combined radiocarbon ( 14 C) analysis with stable isotope analyses ( 13 C and 15 N) to understand feeding habits of soil microarthropods, especially focusing on springtail (Collembola). Most Collembola species exhibited lower Δ 14 C values than litter regardless of their δ 13 C and δ 15 N signatures, indicating their dependence on young carbon. In contrast with general patterns across all taxonomic groups, we found a significant negative correlation between δ 15 N and Δ 14 C values among the edaphic Collembola. This means that the species with higher δ 15 N values depend on C from more recent photosynthate, which suggests that soil-dwelling species generally feed on mycorrhizae to obtain root-derived C. Many predatory taxa exhibited higher Δ 14 C values than Collembola but lower than litter, indicating non-negligible effects of collembolan feeding habits on the soil food web. Our study demonstrated the usefulness of radiocarbon analysis, which can untangle the confounding factors that change collembolan δ 15 N values, clarify animal feeding habits and define the roles of organisms in soil food webs.

Binding of cadmium(II) on soil fulvic acid (FA) was investigated over a range of fulvate-to-cadmium concentration ratios (8 – 59 equiv. mol−1) using 113Cd NMR spectroscopy. The 113Cd chemical shift of cadmium bound on fulvate was observed in a more downfield region (δ −20.4 to −15.6) than that bound on synthetic polymers, poly(acrylic acid) (PAA: δ −36.6 to −38.2), poly(methacrylic acid) (PMAA: δ −34.0 to −25.4), and poly(vinyl benzoic acid) (PVBA: δ −34.7 to −31.2). The calculated values of individual chemical shifts for the species CdL+ and CdL2 (L: carboxylate) formed in Cd(II)–carboxylate systems (e.g., acetate, benzoate) are δ −22 to −24 and δ −39 to −40, respectively. The relative downfield shift of cadmium(II)–fulvate suggests that functional groups (e.g., hydroxyl and neutral N donor) other than carboxylates may be involved in cadmium coordination. The chemical shifts of cadmium complexes of hydroxycarboxylates (e.g., glycolate) or carboxylates containing neutral N donor (e.g., picolinate) were generally observed in more downfield regions than their carboxylate counterparts. Key words: fulvic acid, polyfunctionality, binding sites, chemical shift, 113Cd NMR.

NO₃⁻ showed seasonal and spatial patterns in two human-impacted watersheds. NO₃⁻ is primarily from manure/sewage according to δ¹⁵N and δ¹⁸O. Microbial nitrification took place in the NO₃⁻ of manure/sewage and soil nitrate.

Abstract Aims Competition among plants in a community usually depends on their nitrogen (N)-use efficiency (NUE) and water-use efficiency (WUE) in arid and semi-arid regions. Artemisia frigida is an indicator species in heavily degraded grassland, however, how its NUE and WUE respond to N addition in different successional stages is still unclear, especially with mowing, a common management practice in semi-arid grasslands. Methods Based on a long-term controlled experiment with N addition and mowing in an abandoned cropland from 2006 to 2013, we investigated the NUE and WUE of A. frigida in two patches (i.e. grass and herb patches) in 2013 which represented two potential successional stages from herb to grass communities. The coverage of A. frigida was higher (about 50%) in the herb patch than in the grass patch (about 10%). Stable isotopic C (δ 13C) and N (δ 15N) as well as C and N pools were measured in plants and soils. NUE was calculated as leaf C/N, and leaf δ 13C values were used as a proxy for WUE. Important Findings N addition did not affect WUE of A. frigida, but significantly decreased NUE by 42.9% and 26.6% in grass and herb patches, respectively. The response of NUE to N addition was related to altering utilization of different N sources (NH4+vs. NO3−) by A. frigida according to the changed relationship between leaf δ 15N/soil δ 15N and NUE. Mowing had no effect on NUE regardless of N addition, but significantly increased WUE by 2.3% for A. frigida without N addition in the grass patch. The addition of N reduced the positive effect of mowing on its WUE in grass patch. Our results suggested that decreased NUE and/or WUE of A. frigida under mowing and N addition could reduce its competition, and further accelerate restoration succession from the abandoned cropland to natural grassland in the semi-arid region.

Ecosystem dynamics are driven by both biotic and abiotic processes, and perturbations can push ecosystems into novel dynamical regimes. Plant–plant, plant–soil and mycorrhizal associations all affect plant ecosystem dynamics; however, the direction and magnitude of these effects vary by context and their contribution to ecosystem resilience over long time periods remains unknown. Here, using a mathematical framework, we investigate the effects of plant feedbacks and mycorrhiza on plant–nutrient interactions. We show evidence for strong nutrient controlled feedbacks, moderation by mycorrhiza and influence on ecological resilience. We use this model to investigate the resilience of a longitudinal palaeoecological birch– δ 15 N interaction to plant–soil feedbacks and mycorrhizal associations. The birch– δ 15 N system demonstrated high levels of resilience. Mycorrhiza were predicted to increase resilience by supporting plant–nitrogen uptake and immobilizing excess nitrogen; in contrast, long-term enrichment in available nitrogen by plant–soil feedbacks is expected to decrease ecological resilience.

Abstract. Nitrate loading of coastal ecosystems by rivers that drain industrialised catchments continues to be a problem in the South Eastern North Sea, in spite of significant mitigation efforts over the last 2 decades. To identify nitrate sources, sinks, and turnover in three German rivers that discharge into the German Bight, we determined δ 15N-NO3- and δ18O- NO3- in nitrate and δ 15N of particulate nitrogen for the period 2006–2009 (biweekly samples). The nitrate loads of Rhine, Weser and Ems varied seasonally in magnitude and δ 15N-NO3- (6.5–21‰), whereas the δ 18O-NO3- (-0.3–5.9‰) and δ 15N-PN (4–14‰) were less variable. Overall temporal patterns in nitrate mass fluxes and isotopic composition suggest that a combination of nitrate delivery from nitrification of soil ammonia in the catchment and assimilation of nitrate in the rivers control the isotopic composition of nitrate. Nitrification in soils as a source is indicated by low δ 18O-NO3- in winter, which traces the δ 18O of river water. Mean values of δ 18O-H2O were between –9.4‰ and –7.3‰; combined in a ratio of 2:1 with the atmospheric oxygen δ 18O of 23.5‰ agrees with the found δ 18O of nitrate in the rivers. Parallel variations of δ 15N-NO3- and δ 18O-NO3- within each individual river are caused by isotope effects associated with nitrate assimilation in the water column, the extent of which is determined by residence time in the river. Assimilation is furthermore to some extent mirrored both by the δ 15N of nitrate and particulate N. Although δ 15-NO3- observed in Rhine, Weser and Ems are reflected in high average δ 15N-PN (between 6‰ and 9‰, both are uncorrelated in the time series due to lateral and temporal mixing of PN. That a larger enrichment was consistently seen in δ 15N-NO3- relative to δ 18O-NO3- is attributed to constant additional diffuse nitrate inputs deriving from soil nitrification in the catchment area. A statistically significant inverse correlation exists between increasing δ 15N-NO3- values and decreasing NO3- concentrations. This inverse relationship – observed in each seasonal cycle – together with a robust relationship between human dominated land use and δ 15N-NO3- values demonstrates a strong influence of human activities and riverine nitrate consumption efficiency on the isotopic composition of riverine nitrate.

Abstract. Mountain forests are subject to high rates of physical erosion which can export particulate nitrogen from ecosystems. However, the impact of geomorphic processes on nitrogen budgets remains poorly constrained. We have used the elemental and isotopic composition of soil and plant organic matter to investigate nitrogen cycling in the mountain forest of Taiwan, from 24 sites with distinct geomorphic (topographic slope) and climatic (precipitation, temperature) characteristics. The organic carbon to nitrogen ratio of soil organic matter decreased with soil 14C age, providing constraint on average rates of nitrogen loss using a mass balance model. Model predictions suggest that present day estimates of nitrogen deposition exceed contemporary and historic nitrogen losses. We found ~6‰ variability in the stable isotopic composition (δ15N) of soil and plants which was not related to soil 14C age or climatic conditions. Instead, δ15N was significantly, negatively correlated with topographic slope. Using the mass balance model, we demonstrate that the correlation can be explained by an increase in nitrogen loss by non-fractioning pathways on steeper slopes, where physical erosion effectively removes particulate nitrogen. Published data from forest on steep slopes are consistent with the correlation, demonstrating that variable physical erosion rates can significantly influence soil δ15N, and that particulate nitrogen export is a major loss term in the nitrogen budget of mountain forest.

Abstract. Mountain forests are subject to high rates of physical erosion which can export particulate nitrogen from ecosystems. However, the impact of geomorphic processes on nitrogen budgets remains poorly constrained. We have used the elemental and isotopic composition of soil and plant organic matter to investigate nitrogen cycling in the mountain forest of Taiwan, from 24 sites with distinct geomorphic (topographic slope) and climatic (precipitation, temperature) characteristics. The organic carbon to nitrogen ratio of soil organic matter decreased with soil 14C age, providing constraint on average rates of nitrogen loss using a mass balance model. Model predictions suggest that present day estimates of nitrogen deposition exceed contemporary and historic nitrogen losses. We found ∼6‰ variability in the stable isotopic composition (δ15N) of soil and plants which was not related to soil 14C age or climatic conditions. Instead, δ15N was significantly, negatively correlated with topographic slope. Using the mass balance model, we demonstrate that the correlation can be explained by an increase in nitrogen loss by non-fractioning pathways on steeper slopes, where physical erosion most effectively removes particulate nitrogen. Published data from forests on steep slopes are consistent with the correlation. Based on our dataset and these observations, we hypothesise that variable physical erosion rates can significantly influence soil δ15N, and suggest particulate nitrogen export is a major, yet underappreciated, loss term in the nitrogen budget of mountain forests.

Research Doctorate - Doctor of Philosophy (PhD)
Land application of biowastes including biosolids has been identified as one of the management strategies in soil organic carbon (SOC) sequestration, thereby contributing to potential “direct action” approaches to mitigating climate change. This study aimed to understand the effects of biosolids application on C storage in soils. The specific objectives were to: (i) demonstrate the driving factors and their magnitudes on SOC storage in biosolids amended soils; (ii) examine the effect of co-composting as a feasible strategy to stabilize C in biosolids; (iii) study the effect of biosolid-derived inorganic C (i.e., particulate plastics) on C dynamics and modulation of contaminants in soil, and (iv) to monitor CO2 fluxes and SOC dynamics in biosolids amended soil under field conditions. Firstly, a meta-analysis was conducted to compare quantitatively SOC changes from data derived from 297 field studies over seven variables: soil depth, soil texture, clay content, type of biosolids, application type, time after application (i.e., age) and cumulative biosolids C input rate. A statistical model (i.e., meta-analytic multivariate) was developed to understand the drivers for SOC stock changes resulting from biosolids application. Among the seven variables, the cumulative biosolids C input rate, age, soil depth and type of biosolids were identified as the main drivers of SOC stock change in soil. The highest mean difference for SOC% of 4.7 [3.1–6.4], 95% confidence interval (CI) was observed at 0–15 cm soil depth for a cumulative biosolids C input of 100 Mg ha^-1 at one year after biosolids application. Although years after biosolids application demonstrated a negative relationship with SOC stocks, mineralization of C in biosolids-applied soils is slow, as indicated with the SOC% decrease from 5.0 to 4.4 at 0–15 cm soil depth over five years of 100 Mg ha^-1 biosolids C input. Soil depth illustrated a strong negative effect with SOC stocks decreasing by 1.3% at 0–15 cm soil depth at a cumulative biosolids C input of 100 Mg ha^-1 over a year. Overall, the model estimated an effect of 2.8 SOC% change, indicating that application of biosolids increases SOC stocks and therefore has the potential to be a strategy for soil C sequestration. Secondly, to examine the effect of biosolid-stabilizing materials on C mineralization, biosolids were co-composted with various nanoclay and alkaline materials. Fluidized bed boiler ash (FBA), flue-gas desulphurization gypsum (FGD), red mud (RM), and garden lime were used as the C stabilizing materials. In the co-composting process, biosolids or poultry manure (i.e., biowastes) were mixed with the stabilizing materials at the rate of 10% (w/w) and incubated in an aerobic digester for six months. The stability of C in co-composts was examined by monitoring the decomposition of co-composted biowastes in an arable soil by measuring the release of CO₂, dissolved organic C (DOC) and chemical fractionation of C. The DOC concentrations of final co-composted products were less (~ 20%) in the presence than absence of the amendments, indicating the enhanced stabilization of C in composts in the presence of amendments. In the presence of the stabilizing materials, there was an increase in the non-labile and residual C fractions in the co-composted products. The energy dispersive X-ray (EDX) data for co-composts provided evidence for the association of Ca, Fe and Al with SOC, thereby contributing to the stabilization of C in co-composts. The co-composting of biowaste with the stabilizing materials resulted in ~ 54% decrease in decomposition when applied to soil. There was no significant difference in microbial biomass C (MBC) in soil between the stabilized composts and unamended composts, indicating the C stabilizing materials were unlikely to affect the microbial growth in soil. Stabilized composts increased the priming effect (PE) values in soil, indicating that co-composts enhanced the potential mineralization of SOC. Co-composted biosolids with garden lime and RM were found to be most effective for SOC storage due to their low PE on SOC. Thirdly, a laboratory incubation study examined the effect of biosolid-derived inorganic C (i.e., particulate plastics) on C dynamics and modulation of the toxicity of organic and inorganic contaminants in soil. Particulate plastics (i.e., microplastics) are an inorganic C input to soils resulting from biosolid application. Particulate plastics are also likely to interact with biosolid-derived organic and inorganic contaminants, thereby influencing the microbial functions in soil. Two types of particulate plastics, pristine polyethylene (PPP) and surface modified (BSPP) plastics were used to monitor their impact on microbial activity and C storage in soil. Sandy soil samples were mixed with the two types of particulate plastics at the rate of 6.4% (w/w) in soil. Perfluorooctane sulfonate (PFOS) (1000 μg kg^-1) soil and copper (Cu) (500 mg kg^-1) soil were also used to understand the interactions of particulate plastics and contaminants in relation to C dynamics. After two weeks of the incubation period, soil respiration, MBC, dehydrogenase activity (DHA), and microbial C use efficiency (CUE) were measured. The DHA, MBC, and microbial CUE values were less in contaminated soil treatments than pristine soil, thereby revealing the influence of environmental stress on decreased microbial activity. The microbial activity as measured by the above parameters was higher in the presence than absence of particulate plastics addition. In the Cu-contaminated soil, the CUE was significantly (p < 0.01) higher in particulate plastics treated soils than untreated soils. Moreover, improvement of CUE was observed when particulate plastics were added to the PFOS contaminated soils than control soils. The interactions of particulate plastics with organic and inorganic contaminants were effective in modulating their toxicity to soil microbial function, thereby affecting the SOC storage. Finally, a field study was conducted on two texturally different soils to determine the influence of biosolids application on selected soil chemical properties and CO₂ fluxes. Two sites, located in Manildra (clay loam) and Grenfell (sandy loam), in Australia, were treated at a single level of 70 Mg ha^-1 biosolids. Soil samples were analyzed for SOC fractions. Liquid-state ¹³C and ¹H NMR spectroscopy and FT-IR techniques were used to understand the major constituents present in the humic acid fractions. The natural abundances of soil δ¹³C and δ¹⁵N were measured as isotopic tracers to fingerprint C derived from biosolids. In-situ diurnal CO₂ fluxes, soil moisture, and temperature were also measured using an automated LI-COR LI-8100A soil respirometer. Application of biosolids increased the surface (0–15 cm) SOC by > 45% at both sites, which was attributed to the direct contribution from residual C in the biosolids and also from the increased biomass production. At both sites, application of biosolids increased the non-labile C fraction which indicated the SOC storage potential of biosolids. The spectroscopy results revealed a predominance of aliphatic characteristics in humic acids in biosolids treated soils compared to control soils. Soils amended with biosolids showed depleted δ¹³C, and enriched δ¹⁵N indicating the accumulation of biosolids residual C in soils. The CO₂ flux data indicated that the addition of biosolids was effective in building SOC in both the clay loam and sandy loam soils. In conclusion, the meta-analysis and the field experiments provided evidence for the land application of biosolids as a sustainable strategy to store C in soils. Co-composting biosolids with nanoclay and alkaline materials was found to be suitable for SOC stabilization in soil. Interactions of particulate plastics in biosolids with organic and inorganic contaminants modulated their toxicity to soil microbial activity, thereby improving microbial C use efficiency and SOC storage. The field-based CO₂ flux data indicated that the addition of biosolids was effective in building SOC in soils.

The influence of preparation techniques on the microstructure, grain-size and consequently on the electrical transport properties of the ABO3 structured materials used as electrode and electrolytes in all perovskite IT-SOFC were investigated. Nano-crystalline powders of La1-xMxGa1-yNyO3±δ (M = Sr,; x = −0.10 to 0.15; N = Mg; y = −0.10 to 0.15) (LSGM) as electrolyte, porous La0.8Sr0.2Co0.8Fe0.2O3±δ (LSCF) or LaNi1-xFexO3±δ (x = 0–0.5) (LNF) as cathode, La0.8Sr0.2Cr0.7Mn0.3O3±δ (LSCM) as anode and LaCrO3 or substituted LaCrO 3 as interconnect were synthesized by various wet chemical methods. The wet chemical methods like metal-carboxylate gel decomposition, hydroxide co-precipitation, sonochemical and regenerative sol-gel process followed by microwave sintering of the powders have been used. Microwave sintering parameters were optimized by varying sintering time, and temperature to achieve higher density of LSGM pellets. The phase pure systems were obtained at sintering duration of 30 min at 1200 °C. The XRD, HR-TEM, and SEM measurements revealed the average grain size of these perovskites was ∼ 22 nm range. The electrical conductivities of the compositions were measured by ac (5Hz–13MHz) and dc techniques. The conductivity of the sintered pellets was found to be ∼0.01–0.21 S/cm at 550–1000°C range for electrolyte and 1.5–100 S/cm at 25–1000°C for electrodes respectively. The effect of sonochemical, and regenerative sol-gel methods in processing large quantities of nano-crystalline perovskites with multi-element substitutions at A- and B-sites to achieve physico-chemical compatibility for fabricating zero emission all perovskite IT-SOFCs are reported in this paper.